Drug-eluting implantable medical devices are useful for their ability to provide structural support while medically treating the area in which they are implanted. For example, drug-eluting stents have been used to prevent restenosis in coronary arteries. Drug-eluting stents may administer therapeutic agents such as anti-inflammatory compounds that block local invasion/activation of monocytes, thus preventing the secretion of growth factors that may trigger VSMC proliferation and migration. Other potentially anti-restenotic compounds include antiproliferative agents, such as chemotherapeutics, which include sirolimus and paclitaxel. Other classes of drugs such as anti-thrombotics, anti-oxidants, platelet aggregation inhibitors and cytostatic agents have also been suggested for anti-restenotic use.
Drug-eluting medical devices may be coated with a polymeric material which, in turn, is impregnated with a drug or a combination of drugs. Once the medical device is implanted at a target location, the drug is released from the polymer for treatment of the local tissues. The drug is released by a process of diffusion through a polymer layer of a biostable polymer, and/or as the polymer material degrades when the polymer layer is of a biodegradable polymer.
Drug impregnated polymer coatings are limited in the quantity of the drug to be delivered by the amount of a drug that the polymer coating can carry and the size of the medical device. As well, controlling the rate of elution using polymer coatings is difficult.
Accordingly, drug-eluting medical devices that enable increased quantities of a drug to be delivered by the medical device, and allow for improved control of the elution rate of the drug, and improved methods of forming such medical devices are needed. Co-pending U.S. Patent Application Publication No. 2011/0008405, filed Jul. 9, 2009, U.S. Provisional Application No. 61/244,049, filed Sep. 20, 2009, U.S. Provisional Application No. 61/244,050, filed Sep. 20, 2009, and co-pending U.S. Patent Application Publication No. 2012/0067008, each incorporated by reference herein in their entirety, disclose methods for forming drug-eluting stents with hollow wires. Drug-eluting stents formed with hollow wires can achieve similar elution curves as drug-eluting stents with the therapeutic substance disposed in a polymer on the surface of the stent. Drug-eluting stents formed with hollow wires achieving similar elution curves as drug-polymer coated stent are expected to have similar clinical efficacy while simultaneously being safer without the polymer coating. In addition, a variety of elution curves can be achieved from drug-eluting stents formed with hollow wires. In some applications, such as coronary stents, the diameter of the hollow wire lumen to be filled with the drug or therapeutic substance is extremely small, e.g. about 0.0015 in., which may make filling the lumen difficult. As such, improved apparatus for and methods of filling or loading a therapeutic substance or drug within a lumen of a hollow wire of a stent are needed.